The invention relates to providing backup power to primary power supplies each serving one of several loads.
When several loads, e.g., printed circuit cards, require power, it is sometimes cheaper to provide a separate smaller power supply for each load, rather than one large power supply to serve all loads. In cases where it is crucial to avoid an interruption of power to any of the loads, each primary power supply typically has its own redundant backup power supply. In some cases, the backup and primary supplies are constantly connected in parallel. In other cases, the backup supply is switched in only when the primary supply voltage falls too low.